The present invention relates to tensioning mechanisms and more particularly to a tensioner assembly installable in a food product band saw apparatus for tensioning of a band saw blade.
In the food processing industry large upright band saws such as band saw 10 of FIG. 1 are commonly used for cutting meat products of a variety of sizes. Such band saws typically include a frame 12 upon which is mounted a support surface 14 for positioning meat products to be cut. A housing portion 16 extends above support surface 14 and a housing portion 18 extends below support surface 14. A band saw blade 20 passes though a plane defined by support surface 14 and extends around wheel members (not shown) located with housing portions 16 and 18 for being drivingly rotated by such wheel members. In particular, a drive motor 22 may be connected for rotating a drive wheel in housing portion 18.
In the food processing industry the band saw, including the blade, has to be cleaned each day and each time the food product being cut is changed. Therefore, such band saws preferably include a system which allows easy removal of the saw blade and simple reinstallation and retensioning the saw blade. Further, food product band saws preferably run as quiet as possible since they may operate in supermarket settings. As the noise produced by the band saw can vary according to the tension of the saw blade, it is desirable to enable a user to establish the appropriate saw blade tension in a simple manner. A properly configured tensioner and tensioning system may achieve the above goals.
A tension of the band saw blade may be adjusted by adjusting the position of a drive mount which supports the drive motor 22 and accordingly the drive wheel in housing portion 18. Referring to FIG. 2, and exemplary drive mount 24 is illustrated and is pivotably connectable to a frame 26 of the band saw by pivot pin 28. The drive motor 22 is connected to the drive mount and a drive shaft extends to the lower drive wheel 30 for rotation and support thereof. Thus, the lower drive wheel 30 is also supported by the drive mount 24. A tensioner 32 may be connected between the drive mount 24 at connection point 34 and the frame at a connection point 36, enabling adjustment of the pivotable position of the drive mount 24 and thus the position of the lower drive wheel 30 and/or the tension force of a saw blade 20 extending thereabout.
Tensioner 32 represents a known prior art tensioner which is illustrated schematically in FIG. 3 and includes a mounting bushing 38 with a shaft 40 extending therethrough. A mounting nut 42 is threaded onto the shaft 40 and a spring 44 extends from the mounting bushing 38 to the mounting nut 42. A handle 46 enables rotation of the shaft 40. In operation the mounting bushing 38 is connected to connection point 36 of the frame and the mounting nut 42 is connected to connection point 34 of the drive mount 24. Spring 44 provides a shock and vibration absorbing feature for the lower drive wheel 30 and associated drive motor 22. Tension on the blade (represented schematically at 48) is increased by rotating handle 46 to increase the distance between the mounting bushing 38 and the mounting nut 42. The spring 44 is pre-compressed to assure the blade 48 is properly tensioned when the mounting nut 42 is positioned at the far end of the threaded shaft 40. The pre-compressed force on spring 44 is typically very large since the blade 48 needs a large tension force. To maintain the condition where the handle 46 abuts against the mounting bushing 38 at all times, the spring 44 must be compressed at all times. Unfortunately the compressive force of the spring 44 is largest when the blade 48 is placed in the slack, non-tensioned condition resulting in high spring forces which must be overcome in order to remove the blade 48.
In order to remove a saw blade from a band saw the lower drive wheel 30 must be raised by rotating handle 46 to decrease the distance between the mounting bushing 38 and the mounting nut 42. With the above tensioner 32 arrangement in order to decrease the distance between the mounting bushing 38 and the mounting nut 42 the compression force of the spring 44 must be overcome. Further, the downward weight of the drive motor 22 and lower drive wheel must also be overcome. Accordingly, rotation of the handle 46 can be difficult.
Accordingly, in one embodiment, the present invention is directed to an improved tensioner assembly.
A tensioner assembly includes a mounting bushing having an opening therethrough and a shaft having at least one threaded region along its axial length, the shaft extending through the opening. A mounting nut is threaded onto the shaft. A seating surface extends from the shaft at a position intermediate the mounting bushing and the mounting nut. A spring is disposed around the shaft between the mounting bushing and the seating surface. A first end of the spring is positioned against the seating surface so as to be fixed at the intermediate position along the shaft regardless of a distance between the mounting bushing and the mounting nut, a second end of the spring is positioned toward the mounting bushing.
In another embodiment a method of tensioning a blade of a band saw apparatus including a frame, a drive mount including a first portion pivotably connected to the frame, a rotatable wheel supported by the drive mount and movable therewith, the blade extending about said rotatable wheel, involves: (a) providing a tension bolt assembly including a mounting bushing having an opening therethrough, a shaft extending through the opening and having at least one threaded region along its axial length, a mounting nut threaded onto the threaded region of the shaft and spaced from the mounting bushing, a spring disposed around the shaft and positioned between the mounting bushing and the mounting nut, a first end of the spring positioned against a seating surface located intermediate the mounting bushing and the mounting nut such that said first end of said spring is spaced from the mounting nut, a second end of the spring positioned against a first side of the mounting bushing; (b) connecting the mounting bushing to the frame; (c) connecting the mounting nut to a second portion of the drive mount; and (d) rotating the shaft until the shaft moves through the mounting bushing opening and the spring is compressed, such that a tension force of the blade is balanced with a compression force of the spring.